A crepe paper having crepes, such as tissue paper or toilet paper, is produced by pressing a crepe fiber web against the surface of a heated cylindrical dryer, called a Yankee dryer or Yankee cylinder, which terms will be used interchangeably, so that the crepe fiber web adheres thereto, followed by drying, and then stripping the crepe fiber web or crepe paper from the Yankee dryer using a doctor blade.
In order to form a high-quality crepe paper, the adhesion and strip ability of the crepe fiber web or crepe paper to and from the heated cylindrical dryer are important, and the degrees thereof greatly influence the crepe configuration.
Creping is an important operation in making paper products such as, tissue and towel products. Creping generates softness and necessary void space in tissue and towel products for desirable absorbency. In modern creping operations, it is typical to use compositions comprising adhesives, release agents, modifiers and plasticizers to aid creping operations on a high speed creping machine. The compositions when applied to the surface of a Yankee cylinder or dryer, which terms will be used interchangeably, ensures the wet paper web is transferred smoothly to the hot Yankee dryer. Good adhesion is necessary for the wet paper web to transfer to the Yankee dryer surface. Good adhesion also helps faster drying of the wet paper web by the steam heated Yankee dryer and hot air from an overhead hood. A proper surface application provides adequate adhesion for easy transfer of the wet paper web onto the Yankee cylinder surface.
Once the crepe fiber web on the Yankee cylinder surface is dried, the crepe paper is creped off from the Yankee cylinder surface using a doctor blade. The adhesion should be enough to generate a good crepes structure that will give good handfed properties to the final paper product. However, the adhesion should not be too much that it will hinder the paper web from being creped off from the Yankee cylinder by the doctor blade.
The hardness of the composition used in coating the surface of the Yankee dryer should be in the desirable range. If it is too soft, the surface coating would not be able to protect the Yankee dryer surface from the metal doctor blade. If composition is too hard, the coating on the surface of the Yankee cylinder could start building up causing sheet breaks. A good coating applied to the surface of the Yankee cylinder should provide an optimum range of hardness.
Mills typically use adhesives and release agents in combination to control adhesion of the paper web to the surface of the Yankee cylinder and use one or more modifiers to control the hardness of composition used in coating the surface of the Yankee dryer.
Mills have found using three or more components makes the Yankee creping operation quite complicated. Therefore, tissue and towel manufacturers typically try to use only two agents to control adhesion and hardness of the composition applied to the surface of the Yankee dryer.
Many different hydrophobic materials have been used to improve the release of a paper web from a Yankee cylinder. For example, WO 2011/058086 by Jansen et al talks about application of C16-C20 fatty acids and their salts to a Yankee cylinder to facilitate paper web release from said cylinder. U.S. Pat. No. 7,404,875 by Clugeon, teaches about creping adhesive composition with modifier component comprising limonene. US 2013/0048238 by Glover et al teach the application of oil-based formulations for creping release comprising at least one vegetable oil, at least one lecithin and at least one dispersant/emulsifier. Hydrophobic materials such as naphthenic, paraffinic, vegetable, mineral or synthetic oils and emulsifying surfactants such as fatty acids, alkoxylated alcohols, alkoxylated fatty acids, alkoxylated fatty acids are mentioned as release aids for creping process by Furman et al in U.S. Pat. No. 8,101,045. The application US 2007/0000630 by Hassler, et al. disclose a crepe facilitating composition comprising at least one water-insoluble, non-surface active thermoplastic material having a softening or melting point within a range of 40° C. to 100° C. The list of water-insoluble thermoplastic materials includes montan waxes, paraffin waxes, oxidized waxes, microcrystalline waxes, Carnauba wax, and synthetic waxes produced by Ficher-Trops process.
In addition to hydrophobic agents a wide range of hydrophobic alcohols, glycols, polyethers have been used as creping release agents. For example, U.S. Pat. No. 5,660,687 by Allen et al teaches on creping release aids selected from the group of ethylene glycol, glycerol, propylene glycol, di- and tri-ethylene glycols, dipropylene glycol, polyalkanolamines, aromatic sulfonamides, pyrrolidone and mixtures thereof. The application US 2004/0211534 by Clugeon, et al. talks about application of creping modifier comprising polyoxyalkylene polymers, specifically polyoxypropylene ethers of saturated fatty alcohols. And more recently US 2014/0190644 by Townsend discloses the use of creping release agents comprising a quaternary imidazoline compound, an imidazoline free base, an oil-based dispersion or a combination thereof and a polyether component selected from polypropylene glycol, copolymer or blend of propylene glycol and ethylene glycols.
U.S. Pat. No. 7,744,722 by Tucker et al teaches about application of creping modifier comprising polyethylene to the surface of creping cylinder. The creping modifier further comprises mineral oil, cationic and non-ionic surfactants. U.S. Pat. No. 8,608,904 and U.S. Pat. No. 8,147,649 by the same authors expand the teaching onto applications including oxidized polyethylene in combination with mineral oil and surfactants.
All references mentioned above describe release compositions made by simple blending or emulsification of its components. U.S. Pat. No. 8,883,890 teaches the creping agent formulation comprising nitrogen containing inorganic solid lubricants, e.g. boron nitride and silicon nitride with a particle size of 0.5 to 20 μm. However, the '890 patent teaches that lubricity of creping layer becomes insufficient when the particle size of the lubricant is less than 0.5 μm. The inorganic solid lubricant is dispersed in a creping agent composition at a concentration limited to 0.1 to 5.0% by mass.
The present method teaches the creping properties of a micro-emulsion of a release agent and modifier agent improve upon reduction in particle size. Additionally, the release agents in the present method are stable in a wide range of creping formulations, for example, the hydrophobic agent(s) can range from 0 to about 90% by wt., and can be from about 10% to about 50% by weight of the micro-emulsion.
In addition, the composition should provide good tissue making operation including creping. As mentioned above, if there is a coating or composition buildup, a non-uniform coating, or dryer edge build up, the creping operation could be disrupted.
The present method provides a method for improvement of creping in the manufacturing of creped products such as tissue and towel making processes. It also relates to a single emulsified product of creping release and creping modifier that may contain combination of two or more hydrophobes as well as anionic and non-ionic surfactants.